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POPULATION DYNAMICS – an example from Serengeti, Tanzania 1. What changes in population do we see?

POPULATION DYNAMICS – an example from Serengeti, Tanzania 1. What changes in population do we see? - Censuses 2. What components of the age structure change? - Demography 3. What are the causes of change? - Factors that affect demography. CENSUSES. Changes over time

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POPULATION DYNAMICS – an example from Serengeti, Tanzania 1. What changes in population do we see?

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  1. POPULATION DYNAMICS – an example • from Serengeti, Tanzania • 1. What changes in population do we see? • - Censuses • 2. What components of the age structure change? • - Demography • 3. What are the causes of change? • - Factors that affect demography

  2. CENSUSES • Changes over time 2. Rates of increase

  3. The Serengeti Ecosystem Isuria Scarp Loitaplains KENYA Rift valley Gelai2962 Salai plains TANZANIA Ol DoinyoLengai Serengetiplains Ketumbaine2942 Olduvaigorge Meru4565 Rift valley From Grant Hopcraft

  4. Serengeti Wildebeest Population 1800 1500 1200 Population Size (x 1000) 900 600 300 0 1950 1960 1970 1980 1990 2000

  5. Topi

  6. Impala

  7. Decrease in antelopes of Serengeti

  8. Serengeti Wildebeest Rate of Increase (r)

  9. DEMOGRAPHY 1. Inputs: conceptions births 2. Outputs: mortality 3. Lifetable: age distributions

  10. WILDEBEEST PREGNANCY RATE

  11. Decline following Drought in 1993

  12. Impala recruits 6 months 1 year

  13. Serengeti Warthog Recruitment 2.5 2.0 1.5 Juveniles / Female 1.0 0.5 0.0 1980 1985 1990 1995 2000 2005

  14. WILDEBEEST ADULT MORTALITY Density dependent Inverse density dependent Data from Mduma, Sinclair et al 1999

  15. BUFFALO MORTALITY Density dependent

  16. AFRICAN BUFFALO LIFETABLE

  17. AFRICAN BUFFALO LIFETABLE Age-specific survivorship Age-specific mortality Survivorship

  18. CAUSES OF CHANGE 1. Food 2. Intraspecific competition 3. Interspecific competition • Disease 5. Predation – will deal in later lectures 6. Human hunting

  19. Wildebeest and buffalo grass

  20. Serengeti Grass Growth - Dry season woodlands 9000 6000 Biomass (kg/ha) 3000 0 0 300 600 900 1200 Cumulated Rain (mm)

  21. INTRASPECIFIC COMPETITION Intraspecific competition occurs when there are insufficient resources (e.g. food, space) for all individuals in the population for a part of the year e.g. wildebeest and buffalo in Serengeti dry season

  22. Serengeti Wildebeest per capita Dry Season Food 350 300 250 200 150 100 50 0 1960 1970 1980 1990 2000

  23. Wildebeest adult mortality due to lack of food is density dependent

  24. WILDEBEEST Food protein and bone marrow

  25. INTERSPECIFIC COMPETITION • Between migrating grazers • - with gazelle • - not with zebra • 2. Between migrant and resident grazers • - wildebeest and buffalo

  26. WILDEBEEST, ZEBRA, THOMSON’S GAZELLE Wildebeest Gazelle Zebra

  27. Effects of wildebeest competition

  28. DISEASE • Many diseases appear when animals • have insufficient food and so their • immune systems are impaired. These operate • together with food to cause mortality • 2. Other diseases are Epidemic exotics – • rinderpest virus • 3. Enzootic – distemper from domestic dogs, • rabies. These act more like predators • and will be dealt with later

  29. Serengeti Wildebeest Population Rinderpest removed Data from Mduma & Sinclair

  30. Serengeti Wild Dogs suffered decadal outbreaks of distemper since the 1960s

  31. Conclusions on regulation • Large ungulate species food regulated through • Intraspecific competition • Migrant species food regulated • Small resident ungulate species predator regulated • (see later lecture) • Top predators are food regulated • (Smaller predators are limited by top predators) • Disease works with food under natural conditions • Interspecific competition occurs between the grazers

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